According to PlugInCars, users can sign up for an "all-you-can-eat" plan for unlimited use at $19.99 a month, but pricing has not yet been set for individual charging sessions.

The stations, operated by Aerovironment, will require users to call a toll-free number each time they want to pay for a session via credit card.

Tonia Buell, the project development and communications manager of public-private partnerships with the Washington State Department of Transportation, told PlugInCars that individual sessions could be "somewhere in the neighborhood of $7.50 per DC fast charge and $5.00 for Level 2 use."

Doing the math

The cars using the Electric Highway quick-charging locations are largely Nissan Leafs, plus a smattering of Mitsubishi i-MiEVs (and a few Tesla Model S cars equipped with a CHAdeMO-to-Tesla plug adapter).

In a Leaf, it takes up to 25 minutes to recharge that car's 24-kilowatt-hour battery pack to 80 percent--giving it a range of about 65 miles. (Due to the nature of cell charging, getting the last 20 percent recharged takes considerably longer.)

Translated to compare to gasoline prices--assuming a gas cost of $3.75 per gallon--that would make quick-charging an electric car roughly the same cost as the fuel cost for a 33-mpg vehicle.

That may not seem unreasonable to electric-car drivers on occasional long trips, who otherwise charge overnight at home, at much cheaper rates.

But the ability of Tesla Model S cars with far larger battery packs to recharge at CHAdeMO stations using an adapter raises the concern that Teslas would occupy a DC fast-charging location for much longer, drawing more energy--for the same price.

Level 2: not for long trips

Each of Washington's 12 locations has both a DC quick charger and a 240-Volt Level 2 charging station, which can add roughly 20 miles of range to a 2013 or 2014 Nissan Leaf every hour.

On the surface, a $5 cost for a Level 2 session seems a less appealing proposition.

Unless a Leaf driver just needs to "top up" the car's charge--in which case the per-kWh cost is very high against home charging--the owner would have to plan on spending one to four hours at the charging location for the next leg of a longer trip.

Meanwhile, Tesla continues to expand its own Supercharger network of DC fast-charging stations, with more than 80 live as of today and ambitious plans to cover much of the U.S. by the end of next year.

And Supercharger use is free to any Tesla Model S owner--no fees at all for an 80-percent recharge (or 200-plus miles) in 20 minutes.

Tesla has the advantage of a single system that it controls, and a known user base.

The issue of public charging stations funded by a diverse group of public and private entities must seem ugly and complex from the company's Silicon Valley headquarters.

Business model debatable

Both Oregon and British Columbia will ultimately face the challenge of how to fund their public charging networks as well.

It rather raises the question of whether Tesla is quietly chuckling at the travails of those who must figure out whether there's any business model at all for charging electric-car drivers to use charging stations.

What are your thoughts on how public charging for electric cars should be paid for?